Method for guiding a crack in the peripheral region of a donor substrate

ABSTRACT

The present invention relates to a method for separating solid-body slices ( 1 ) from a donor substrate ( 2 ). The method comprises the steps of: producing modifications ( 10 ) within the donor substrate ( 2 ) by means of laser beams ( 12 ), wherein a detachment region is predefined by the modifications ( 10 ), along which detachment region the solid-body layer ( 1 ) is separated from the donor substrate ( 2 ), and removing material from the donor substrate ( 2 ), starting from a surface ( 4 ) extending in the peripheral direction of the donor substrate ( 2 ), in the direction of the centre (Z) of the donor substrate ( 2 ), in particular in order to produce a peripheral indentation ( 6 ).

The present invention, according to claim 1, relates to a method forseparating solid-body slices from a donor substrate.

In many technical fields (for example microelectronics or photovoltaictechnology), materials such as silicon, germanium or sapphire are oftenused in the form of thin slices and plates (what are known as wafers).As standard, wafers of this kind are currently produced by sawing froman ingot, with relatively large material losses (“kerf loss”) beingsustained. Since the used starting material is often very costly, it ishighly sought to produce wafers of this kind with less materialconsumption, and therefore more efficiently and more economically.

By way of example, with the currently conventional methods, almost 50%of the used material is lost as “kerf loss” in the production of siliconwafers for solar cells alone. Considered globally, this corresponds toan annual loss of more than 2 billion euros. Since the costs of thewafer account for the largest share of the cost of the finished solarcell (over 40%), the costs of solar cells could be significantly reducedby corresponding improvements in the wafer production.

Methods which dispense with the conventional sawing and for example candirectly split off thin wafers from a thicker workpiece by use oftemperature-induced stresses appear to be particularly attractive forwafer production of this kind without kerf loss (“kerf-free wafering”).These include in particular methods as described for example inPCT/US2008/012140 and PCT/EP2009/067539, where a polymer layer appliedto the workpiece is used in order to produce these stresses.

With use of the methods according to the prior art, the produced wafersusually have greater thickness variations, wherein the spatial thicknessdistribution often presents a pattern having tetramerous symmetry. Thetotal thickness variation (TTV) as considered over the entire wafer,with use of the previous methods, is often more than 100% of the averagewafer thickness (a wafer for example of 100 micrometres averagethickness, which for example at its thinnest point is 50 micrometresthick and at its thickest point is 170 micrometres thick, has a TTV of170-50=120 micrometres, which corresponds to a total thickness variationof 120% relative to its average thickness). Wafers with high thicknessvariations of this kind are not suitable for many applications. Inaddition, in the most frequently occurring tetramerous thicknessdistribution patterns, the regions with the greatest fluctuations aredisposed unfortunately in the middle of the wafer, where they are themost disruptive.

Here, crack formation is particularly critical, since solid-body sliceswith a low TTV can be directly produced only with very precise crackformation.

It has been found that modifications for specifying the course of thecrack at a distance from the edge of the solid body can indeed beproduced in a solid body by means of LASER beams, however this is notreadily possible in the region of the edge of a solid body on account ofedge effects. If the middle of the LASER focus directly contacts theedge of the material, one half of the beam thus contacts the solid bodywith finite extent, and the other half runs into the air. On account ofthe difference in refractive index, this causes damage at the side ofthe solid body, way beyond the actually intended damage layer afterrefractive index correction. Since, in addition, only half or a fractionof the LASER radiation is coupled into the material, the damage at theedge is reduced compared to in the middle of the solid body. Thisreduced damage causes the crack to be distorted over its course at theedge or means that the crack does not progress in the laser plane.

The object of the present invention is therefore to provide a methodthat enables the production of wafers having a low TTV.

The aforementioned object is achieved by a method according to claim 1.The method according to the invention for separating at least onesolid-body layer, in particular a solid-body slice, from a donorsubstrate preferably comprises at least the following steps: providing adonor substrate, producing modifications within the donor substrate bymeans of LASER beams, wherein a detachment region is predefined by themodifications, along which detachment region the solid-body layer isseparated from the donor substrate, removing material from the donorsubstrate, starting from a surface extending in the peripheral directionof the donor substrate, in the direction of the centre of the donorsubstrate, in particular in order to produce a peripheral indentation,wherein the detachment region is exposed by the material removal,separating the solid-body layer from the donor substrate, wherein thedonor substrate is weakened in the detachment region by themodifications in such a way that the solid-body layer detaches from thedonor substrate, or such a number of modifications are produced that thedonor substrate is weakened in the detachment region in such a way thatthe solid-body layer detaches from the donor substrate or astress-inducing layer is produced in or arranged on a surface of thedonor substrate, in particular a planar surface, oriented at an inclinerelative to the peripheral surface, and mechanical stresses are producedin the donor substrate by a thermal treatment of the stress-inducinglayer, wherein the mechanical stresses produce a crack for separating asolid-body layer, which crack propagates along the modifications,starting from the surface of the donor substrate exposed by the materialremoval.

This solution is advantageous since an edge of the donor substrate, inthe region of which modifications for further forming of the detachmentregion can be produced only in a very complex manner, can be removed orreduced or modified. A radial material removal is thus hereby provided,as a result of which the distance of the peripheral surface from thedetachment region is reduced.

Further preferred embodiments are the subject of the dependent claimsand/or the following parts of the description.

The detachment region predefined by the modifications, in accordancewith a further preferred embodiment of the present invention, isdistanced further from the peripheral surface of the donor substratebefore the material removal than after the material removal. Thisembodiment is advantageous since the detachment region thus can beeasily produced and yet is still preferably adjacent to the outerperipheral surface of the donor substrate after the material removal.

The modifications for predefining the detachment region, in accordancewith a further preferred embodiment of the present invention, areproduced before the material removal, and, by means of the materialremoval, a reduction of the distance of the detachment region to lessthan 10 mm, in particular to less than 5 mm and preferably to less than1 mm, is achieved at least at specific points, or the modifications forpredefining the detachment region are produced after the materialremoval, wherein the modifications are produced in such a way that thedetachment region is distanced, at least at specific points, by lessthan 10 mm, in particular less than 5 mm, and preferably less than 1 mm,from a surface exposed by the material removal. At least individualmodifications of the detachment region are particularly preferably partof the surface of the donor substrate that is exposed by the materialremoval and that is peripheral at least in part, preferably completely.

In accordance with a further preferred embodiment of the presentinvention, the material is removed by means of ablation beams, inparticular ablation LASER beams, or ablation fluids, or an indentationwith an asymmetrical design is produced by the material removal, or thematerial removal is performed at least in portions in the peripheraldirection of the donor substrate as a reduction of the radial extent ofthe donor substrate, in the entire region between the detachment regionand a surface of the donor substrate distanced homogeneously from thedetachment region.

The aforementioned object can be achieved additionally or alternativelyby a method for separating solid-body slices from a donor substrate,said method preferably comprising at least the following steps:providing a donor substrate, removing material from the donor substrate,starting from a surface extending in the peripheral direction of thedonor substrate, in the direction of the centre of the donor substratein order to produce an indentation, wherein the material is removed bymeans of ablation LASER beams and/or the indentation is producedasymmetrically, producing modifications by means of further LASER beamswithin the donor substrate, wherein the modifications are positioned insuch a way that they are adjacent to the indentation, wherein thesolid-body slice detaches from the donor substrate by the producedmodifications or a stress-inducing layer is produced or arranged on asurface of the donor substrate which is oriented at an incline relativeto the peripheral surface and in particular is planar, and mechanicalstresses are produced in the donor substrate by a thermal treatment ofthe stress-inducing layer, wherein the mechanical stresses produce acrack for separating a solid-body layer, which crack propagates alongthe modifications, starting from the indentation.

The modifications are achieved here preferably using the shortestpossible pulses in the smallest possible vertical region by focusing inthe material with a high numerical aperture.

During the ablation, the ablation LASER beams are focused on the surfaceof the material with a lower numerical aperture and often a wavelengthabsorbed linearly by the material. The linear absorption of the ablationLASER beams at the material surface leads to an evaporation of thematerial (the ablation), i.e. to a material removal, and not only to astructural change.

This solution is advantageous since an edge region of the donorsubstrate is processed by means of a material-removing treatment, bymeans of which the outer edge of the donor substrate is displaced, inthe region of the plane in which the crack propagates, towards thecentre of the donor substrate. The displacement preferably occurs in thedirection of the centre to such an extent that all LASER beams canpenetrate the donor substrate over the same planar surface, depending onthe penetration depth of the LASER beams and/or the angle of the LASERbeams to one another.

The indentation surrounds the donor substrate, in accordance with afurther preferred embodiment of the present invention, completely in theperipheral direction. This embodiment is advantageous since the crackcan be introduced into the donor substrate in a defined manner over theentire periphery of the donor substrate.

In accordance with a further preferred embodiment of the presentinvention, the indentation runs towards the centre as far as anindentation end that becomes increasingly narrower, in particular in awedge-like or V-shaped manner, wherein the indentation end lies in theplane in which the crack propagates. This embodiment is advantageoussince a notch is created by the indentation end, which notch predefinesthe direction of propagation of the crack.

The asymmetric indentation, in accordance with a further preferredembodiment of the present invention, is produced by means of a grindingtool, which is negatively shaped at least in part in order to make theindentation. This embodiment is advantageous since the grinding tool canbe produced in accordance with the edge or indentation to be formed.

In accordance with a further preferred embodiment of the presentinvention, the grinding tool has at least two differently shapedprocessing portions, wherein a first processing portion is intended forprocessing of the donor substrate in the region of the underside of asolid-body slice to be separated and a second processing portion isintended for processing of the donor substrate in the region of theupper side of the solid-body slice to be separated from the donorsubstrate. This embodiment is advantageous since, in addition toshapings for improved crack formation, shapings for improved handlingcan also be produced by means of the grinding tool at the same time orat a different time on the donor substrate or on the portions of thedonor substrate forming one or more solid-body slices.

In accordance with a further preferred embodiment of the presentinvention, the first processing portion produces a deeper orlarger-volume indentation in the donor substrate than the secondprocessing portion, wherein the first processing portion and/or thesecond processing portion have/has curved or straight grinding faces.The first processing portion preferably has a curved main grinding faceand the second processing portion preferably likewise has a curvedsecondary grinding face, wherein the radius of the main grinding face isgreater than the radius of the secondary grinding face, the radius ofthe main grinding face is preferably at least twice as large as theradius of the secondary grinding face, or the first processing portionhas a straight main grinding face and the second processing portion hasa straight secondary grinding face, wherein, by means of the maingrinding face, more material is removed from the donor substrate thanwith the secondary grinding face, or the first processing portion has astraight main grinding face and the second processing portion has acurved secondary grinding face, or the first processing portion has acurved main grinding face and the second processing portion has astraight secondary grinding face.

The grinding tool preferably has a multiplicity of processing portions,in particular more than 2, 3, 4, 5, 6, 7, 8, 9 or 10 processingportions, in order to process a corresponding multiplicity of portionsof the donor substrate, which can be associated with differentsolid-body slices, in a machining or material-removing manner.

In accordance with a further preferred embodiment of the presentinvention, the ablation LASER beams are produced with a wavelength inthe range between 300 nm (UV ablation with frequency-tripled Nd:YAG orother solid-body laser) and 10 μm (CO₂ glass laser, often used forengraving and cutting processes), with a pulse length of less than 100microseconds and preferably less than 1 microsecond, and particularlypreferably less than 1/10 of a microsecond, and with a pulse energy ofmore than 1 μJ and preferably more than 10 μJ. This embodiment isadvantageous since the indentation can be produced by means of a LASERdevice and not by means of a grinding tool, which becomes worn.

The modifications in the donor substrate are produced in amaterial-dependent manner preferably with the following configurationsor LASER parameters: If the donor substrate consists of silicon or thedonor substrate comprises silicon, then nanosecond pulses or shorter(<500 ns), a pulse energy in the microjoule range (<100 μJ), and awavelength >100 nm are preferably used.

In the case of all other materials and material combinations, a pulse <5picoseconds, pulse energies in the microjoule range (<100 μJ), andwavelengths variable between 300 nm and 2500 nm are preferably used.

It is important here that a large aperture is provided in order to passdeep into the material. The aperture for producing the modificationswithin the donor substrate is therefore preferably larger than theaperture for ablation of material by means of the ablation LASER beamsfor producing the indentation. The aperture is preferably multiple timeslarger, in particular at least 2, 3, 4, 5 or 6 times larger, than theaperture for ablation of material by means of the ablation LASER beamsfor producing the indentation. The size of the focus for producing amodification, in particular with regard to the diameter of the focus, ispreferably smaller than 10 μm, preferably smaller than 5 μm, andparticularly preferably smaller than 3 μm.

Alternatively, the present invention can relate to a method forseparating solid-body slices from a donor substrate. Here, the methodaccording to the invention preferably comprises at least the followingsteps: providing a donor substrate, producing modifications within thedonor substrate by means of LASER beams, wherein the LASER beamspenetrate the donor substrate over a planar surface of the donorsubstrate, wherein the totality of LASER beams is inclined relative tothe surface of the donor substrate in such a way that a first portion ofthe LASER beams penetrates the donor substrate at a first angle to thesurface of the donor substrate and at least one further portionpenetrates the donor substrate at a second angle to the surface of thedonor substrate, wherein the value of the first angle differs from thevalue of the second angle, wherein the first portion of the LASER beamsand the second portion of the LASER beams are focused in the donorsubstrate in order to produce the modification, wherein the solid-bodyslice detaches from the donor substrate by the produced modifications ora stress-inducing layer is produced or arranged on the planar surface ofthe donor substrate and mechanical stresses are produced in the donorsubstrate by a thermal treatment of the stress-inducing layer, wherein acrack for separating a solid-body layer is produced by the mechanicalstresses and propagates along the modifications. The donor wafer and/orthe LASER device emitting the LASER beams are/is preferably rotatedabout an axis of rotation during the production of the modifications.Additionally or alternatively to the rotation of the donor wafer, thedistance of the LASER beams from the centre of the donor wafer isparticularly preferably changed.

The totality of LASER beams, in accordance with a further preferredembodiment of the present invention, is oriented in the same orientationrelative to the planar surface of the donor substrate for the productionof modifications in the region of the centre of the donor substrate andfor the production of modifications in the region of an edge of thedonor substrate provided in the radial direction.

This solution is advantageous since the total cross-section of the laserbeam upon entry into the solid body contacts a planar surface, and sincehomogeneous damage then occurs in the depth. This homogeneous damage canbe produced as far as the outer edge of the donor substrate extending inparticular orthogonally to the planar surface. The modifications in theedge region of the donor substrate and in the region of the centre ofthe donor substrate can thus be produced by means of one processingstep.

In accordance with a further preferred embodiment of the presentinvention, the first portion of the LASER beams penetrates the donorsubstrate at a first angle to the surface of the donor substrate and thefurther portion of the LASER beams penetrates at a second angle forproduction of modifications in the region of the centre of the donorsubstrate and for production of modifications in the region of an edgeof the donor substrate provided in the radial direction, wherein thevalue of the first angle always differs from the value of the secondangle. The first angle and the second angle are preferably constant orunchanged or are not actively changed during the production of themodifications. This embodiment is advantageous since

In accordance with a further preferred embodiment of the presentinvention, the LASER device comprises a femtosecond LASER (fs LASER) ora picosecond LASER (ps LASER), and the energy of the LASER beams of theLASER (fs LASER or ps LASER) is preferably selected in such a way thatthe propagation of damage of each modification in the top layer and/orthe sacrificial layer is less than 3 times the Rayleigh length,preferably less than the Rayleigh length, and particularly preferablyless than a third of the Rayleigh length and/or the wavelength of theLASER beams of the fs LASER is selected in such a way that theabsorption of the top layer and/or of the sacrificial layer is less than10 cm⁻¹ and preferably less than 1 cm⁻¹ and particularly preferably lessthan 0.1 cm⁻¹ and/or the individual modifications are produced in eachcase as a result of a multi-photon excitation brought about by the fsLASER.

In accordance with a further preferred embodiment of the presentinvention the LASER beams for producing the modifications penetrate thedonor wafer over a surface that is part of the solid-body slice to beseparated. This embodiment is advantageous since the donor substrate isheated to a lesser extent, whereby the donor substrate is exposed onlyto low thermal stresses.

In accordance with a further preferred embodiment of the presentinvention, the ablation radiation comprises accelerated ions and/orplasma and/or LASER beams and/or is formed by electron beam heating orultrasound waves and/or is part of a lithographic method (electron beam,UV, ions, plasma) with at least one etching step following a previouslyexecuted photoresist coating and/or the ablation fluid is a liquid jet,in particular a water jet of a water jet cutting process.

The stress-inducing layer, in accordance with a further preferredembodiment of the present invention, comprises a polymer, in particularpolydimethylsiloxane (PDMS), or consists thereof, wherein the thermaltreatment is preferably performed in such a way that the polymerexperiences a glass transition, wherein the stress-inducing layer istemperature-controlled, in particular by means of liquid nitrogen, to atemperature below room temperature (i.e. to a temperature below 20° C.)or below 0° C. or below −50° C. or below −100° C. or below −110° C., inparticular to a temperature below the glass transition temperature ofthe stress-inducing layer.

This embodiment is advantageous since it has been found that, due to thethermal treatment of the stress-inducing layer, in particular byutilisation of the property changes of the material of thestress-inducing layer occurring with the glass transition, the forcesnecessary to initiate and form a crack can be produced in a donorsubstrate.

The donor substrate preferably comprises a material or a materialcombination from one of the main groups 3, 4 and 5 of the Periodic Tableof Elements, such as Si, SiC, SiGe, Ge, GaAs, InP, GaN, Al2O3(sapphire), AlN, or consists of one or more of these materials. Thedonor substrate particularly preferably comprises a combination ofelements occurring in the third and fifth group of the Periodic Table ofElements. Conceivable materials or material combinations are for examplegallium arsenide, silicon, silicon carbide, etc. Furthermore, the donorsubstrate can comprise a ceramic (for example Al2O3—aluminium oxide) orcan consist of a ceramic, preferred ceramics being for exampleperovskite ceramics (such as Pb—, O—, Ti/Zr— containing ceramics) ingeneral, and lead magnesium niobates, barium titanate, lithium titanate,yttrium aluminium garnet, in particular yttrium aluminium garnetcrystals for solid-body laser applications, SAW (surface acoustic wave)ceramics, such as lithium niobate, gallium orthophosphate, quartz,calcium titanate, etc., in particular. The donor substrate thuspreferably comprises a semiconductor material or a ceramic material, orthe donor substrate particularly preferably consists of at least onesemiconductor material or a ceramic material. It is also conceivablethat the donor substrate comprises a transparent material or partiallyconsists of or is made of a transparent material, such as sapphire.Further materials which can be considered here as solid-body materialalone or in combination with another material are for example “wide bandgap” materials, InAlSb, high-temperature superconductors, in particularrare earth cuprates (for example YBa2Cu3O7).

The subject matter of patent application DE 2013 205 720.2 with thetitle: “Method for rounding edges of semiconductor parts produced from asemiconductor starting material, and semiconductor products produced bythis method” is hereby incorporated by reference in its full extent inthe subject matter of the present description.

The use of the word “substantially” in all cases in which this word isused within the scope of the present invention preferably defines adeviation in the range of 1% to 30%, in particular 1% to 20%, inparticular 1% to 10%, in particular 1% to 5%, in particular 1% to 2%,from the definition that would be given without the use of this word.

Further advantages, objectives and properties of the present inventionwill be explained on the basis of drawings accompanying the followingdescription, in which the solutions according to the invention areillustrated by way of example. Components or elements or method steps ofthe solutions according to the invention which in the figures coincideat least substantially in terms of their function can be denoted here bythe same reference signs, wherein these components or elements do nothave to be provided with reference signs or explained in all figures.

IN THE DRAWINGS

FIG. 1 shows a first example of an edge treatment within the scope ofthe solid-body slice production according to the invention;

FIG. 2 shows examples of contours of grinding tools as can be used inaccordance with the method shown in FIG. 1;

FIG. 3 shows a second example of an edge treatment within the scope ofthe solid-body slice production according to the invention; and

FIGS. 4a-4d show a third example of an edge treatment within the scopeof the solid-body slice production according to the invention;

FIGS. 5a-5b show an illustration of a problem occurring when producingmodifications by means of LASER beams in the edge region of a donorsubstrate; and

FIG. 6 shows a schematic illustration of a solid body that hasindentations covered or superimposed or closed by a stress-inducinglayer.

FIG. 1 shows 5 illustrations, by means of which examples of thesolid-body slice production or wafer production according to theinvention are shown. Illustration 1 shows a grinding tool 22, which hastwo processing portions 24 distanced from one another, which each form amain grinding face 32. The main grinding faces 32 are formed here sothat they produce indentations 6 in a donor substrate 2. The grindingtool 22 is preferably formed as a rotary grinding tool or as a beltgrinding tool.

Illustration 2 of FIG. 1 shows a donor substrate 2, in whichindentations 6 have been produced by means of the grinding tool 22.Here, the indentations 6 are distanced preferably uniformly from oneanother in the longitudinal direction of the donor wafer 2, wherein itis also conceivable for the distances to be of different sizes. Inaccordance with the second illustration in FIG. 2, modifications 10 arealso produced in the donor substrate 2 by means of a LASER device 46.The LASER device 46 for this purpose emits LASER beams 12, whichpenetrate the donor substrate 2 over a preferably planar surface 16 ofthe donor substrate 2, and a modification 10 of the lattice structure ofthe solid body or of the donor substrate 2 is produced or brought aboutat a focus point 48, in particular by a multi-photon excitation. Here,the modification 10 is preferably a material conversion, in particular aconversion of the material into another phase, or a materialdegradation.

The third illustration shows that a stress-inducing layer 14 has beenproduced or arranged on the surface 16 over which the LASER beams 12were introduced into the donor substrate 2 for production of themodifications 10. The stress-inducing layer 14 is thermally treated ortemperature-controlled, in particular cooled, in order to producemechanical stresses in the donor substrate 2. By means of the thermaltreatment of the stress-inducing layer 14, the stress-inducing layer 14contracts, whereby the mechanical stresses are produced in the donorsubstrate 2. The previously produced indentations 6 form notches,through which the mechanical stresses can be conducted in such a waythat the crack 20 resulting from the stresses propagates in a targetedmanner in the region of crack formation predefined by the modifications10. The indentation ends 18 therefore are preferably adjacent to therespective regions of crack formation predefined by the modifications10. It is preferably always the case that only precisely the solid-bodylayer 1 of which the indentation 6 is distanced least far from thestress-inducing layer 14 is split off.

Illustration 4 shows a state following crack propagation. The solid-bodyslice 1 has been split off from the donor substrate 2, and thestress-inducing layer 14 initially still remains on the surface 16 ofthe solid-body slice 1.

Reference sign 28 denotes the side of the solid-body slice 1 which isdenoted here as the underside of the solid-body slice 1, and referencesign 30 denotes the side of the solid-body slice 1 which is denoted hereas the upper side of the solid-body slice 1.

Illustration 5 shows a method in which the solid-body layer 1 detachesfrom the donor substrate 2 without a stress-inducing layer 14. Here,following production of the indentation 6, so many modifications 10 arepreferably produced by means of LASER beams 12, that the solid-bodylayer 1 detaches from the donor substrate 2. The dashed line Z herepreferably characterises a centre or an axis of rotation of the donorsubstrate 2. The donor substrate 2 is preferably rotatable about theaxis of rotation Z.

FIG. 2 shows two illustrations, wherein each illustration shows agrinding tool 22 with a specific contour. If reference is made to aplanar, straight or curved portion with regard to the grinding tool,this is always understood to mean a portion of the shown contour. Ofcourse, the grinding tool 22 can be formed for example as a rotarygrinding tool, whereby the portions adjacent to the contour in theperipheral direction would preferably extend in a curved manner in theperipheral direction. The grinding tool 22 shown in the firstillustration of FIG. 2 has a first processing portion 24, which has acurved main grinding face 32, and has a second processing portion 26,which has a curved secondary grinding face 34, wherein the radius of themain grinding face 32 is greater than the radius of the secondarygrinding face 34, preferably the radius of the main grinding face 32 isat least twice, three times, four times or five times as great as theradius of the secondary grinding face 34.

In accordance with the second illustration of FIG. 2, the firstprocessing portion 24 of the grinding tool 22 has a straight maingrinding face 32 and the second processing portion 26 has a straightsecondary grinding face 34, wherein more material is removed from thedonor substrate 2 by means of the main grinding face 32 than by means ofthe secondary grinding face 34.

The grinding tools 22 shown in FIG. 2 and the indentations produced bythe shown grinding tools 22 can likewise be used in respect of theillustrations shown in FIG. 1.

FIG. 3 shows a further variant of the method according to the invention.By means of a comparison of the first and fifth illustration, it can beseen that the modifications 10 produced by means of the LASER beams 12,in the case of a planar surface 16, can be produced closer to the edge44 than if the tip of the edge 17 of the surface 16 is removed, as shownin the fifth illustration. The LASER beams 12 here penetrate the donorsubstrate 2, similarly to the modification production explained withreference to FIG. 1.

The second illustration of FIG. 3 shows the production of an indentation6 starting from a peripheral surface 4 in the direction of the centre Zof the donor substrate 2, wherein the indentation is produced by meansof ablation LASER beams 8 of an ablation LASER (not shown). The ablationLASER beams 8 here preferably evaporate the material of the donorsubstrate 2 in order to produce the indentation 6.

Illustration 3 of FIG. 3 corresponds substantially to illustration 3 ofFIG. 2, wherein merely the form of the indentation here is notasymmetrical, but instead is symmetrical. In accordance with thisillustration as well, a stress-inducing layer 14 is thus produced orarranged on the donor substrate 2 and is thermally treated, inparticular by means of liquid nitrogen, in order to produce mechanicalstresses for initiating a crack 20.

Illustration 4 of FIG. 3 shows the solid-body slice 1 split off from thedonor substrate 2, with the stress-inducing layer still arranged on saidsolid-body slice.

It can also be seen from illustration 5 of FIG. 3 that in the case of adonor substrate 2 of which the tip of the edge 17 is processed, theindentation 6 to be produced by means of ablation LASER beams 8 mustreach further in the direction of the centre of the donor substrate 2than if the tip of the edge 17 is not processed. Here, however, it isalso conceivable that the indentation is not produced by means ofablation LASER beams 8, but instead by means of a grinding tool 22 (asis known for example from FIGS. 1 and 2).

FIG. 4a shows an additional or alternative solution according to theinvention for the separation of solid-body layers 1 from a donorsubstrate 2. In accordance with FIG. 4a , a detachment region 11 isproduced within the donor substrate 2. The modifications 10 arepreferably distanced here from a peripheral delimiting face 50 of thedonor substrate 2. The modifications 10 are preferably producedsimilarly to illustration 2 of FIG. 1. Here, it is conceivable that theLASER beams 12 are introduced into the donor substrate 2 from below orfrom above, i.e. over the surface 16.

FIG. 4b schematically shows the processing of the donor substrate 2 bymeans of an ablation tool 22, in particular a tool for machining thedonor substrate 2, such as a grinding tool 22. By means of theprocessing, material is removed, at least in portions in the peripheraldirection of the donor substrate 2, in the entire region between thedetachment region and a surface of the donor substrate 2 distancedpreferably homogeneously, in particular in parallel, from the detachmentregion, for reduction of the radial extent of the donor substrate 2. Thematerial is preferably removed in an annular manner, in particular witha constant or substantially constant radial extent.

FIG. 4c shows an example of a state after the removal of the material.Here, it is conceivable for example that the material is removed in theaxial direction of the donor substrate 2 up to the detachment plane, ortherebeneath or thereabove.

FIG. 4d shows a state following the separation or detachment of thesolid-body layer 1 from the donor substrate 2.

FIGS. 5a and 5b show a problem in the edge region of the donor substrate2 occurring with the production of modifications by means of LASER beams12. By means of the different refractive indices in the air and in thedonor substrate, the LASER beam portions 38, 40 of a LASER beam 12 donot coincide exactly with one another, thus resulting in undesirableeffects, such as the production of defects at undesirable locations, anundesirable local heating, or a prevention of the production of amodification.

FIG. 5b shows that a problem-free production of modifications 10 can beprovided only if the modification 10 to be produced is distanced fromthe peripheral surface of the donor substrate 2 to such an extent thatboth LASER beam portions 38, 40 are each refracted through material withthe same refractive index and preferably over the same distance.However, this means that the production of the modification, as itoccurs in the region distanced from the edge region, cannot be readilyextended to the edge region.

The present invention thus relates to a method for separating solid-bodyslices 1 from a donor substrate 2. Here, the method according to theinvention comprises the following steps:

providing a donor substrate 2, removing material from the donorsubstrate 2, starting from a surface 4 extending in the peripheraldirection of the donor substrate 2, in the direction of the centre Z ofthe donor substrate 2 in order to produce an indentation 6, wherein thematerial is removed by means of ablation LASER beams 8 and/or theindentation 6 is produced asymmetrically, producing modifications 10within the donor substrate 2 by means of further LASER beams 112,wherein the modifications 10 are positioned in such a way that they areadjacent to the indentation 6, wherein the solid-body slice 1 detachesfrom the donor substrate 2 by means of the produced modifications 10, ora stress-inducing layer 14 is produced or arranged on a surface 16 ofthe donor substrate 2, which surface is oriented at an incline to theperipheral surface and in particular is planar, and mechanical stressesare produced in the donor substrate 2 by a thermal treatment of thestress-inducing layer 14, wherein the mechanical stresses produce acrack 20 for separating a solid-body layer 1, which crack propagatesalong the modifications 10, starting from the indentation 6.

The present invention thus relates to a method for separating solid-bodyslices 1 from a donor substrate 2. Here, the method according to theinvention comprises the following steps:

producing modifications 10 within the donor substrate 2 by means ofLASER beams 12, wherein a detachment region is predefined by themodifications 10, along which detachment region the solid-body layer 1is separated from the donor substrate 2,

removing material from the donor substrate 2, starting from a surface 4extending in the peripheral direction of the donor substrate 2 in thedirection of the centre Z of the donor substrate 2, in particular inorder to produce a peripheral indentation 6, wherein the detachmentregion is exposed by the material removal, separating the solid-bodylayer from the donor substrate, wherein the donor substrate is weakenedin the detachment region by the modifications in such a way that thesolid-body layer 1 detaches from the donor substrate 2 as a result ofthe material removal or such a number of modifications are producedafter the material removal that the donor substrate is weakened in thedetachment region in such a way that the solid-body layer 1 detachesfrom the donor substrate 2 or a stress-inducing layer 14 is produced orarranged on a surface 16 of the donor substrate 2, which surface isoriented at an incline to the peripheral surface and in particular isplanar, and mechanical stresses are produced in the donor substrate 2 bya thermal treatment of the stress-inducing layer 14, wherein themechanical stresses produce a crack for separating a solid-body layer 1,which crack propagates along the modifications 10, starting from thesurface of the donor substrate exposed by the material removal.

FIG. 6 schematically shows an arrangement in accordance with which thestress-inducing layer 14 preferably superimposes or covers or closes atleast one indentation 6, in particular a recess or hollow cavity, whichextends preferably starting from a planar or substantially planarsurface 16 in the direction of a further surface of the solid body 2,which further surface is preferably parallel to the planar surface 16.

The stress-inducing layer 14 is preferably produced as a polymer layeror is produced as a layer that consists predominantly in terms ofproportions by mass and/or proportions by volume of at least one polymermaterial. The surface 16 on which the stress-inducing layer 14 isarranged preferably has treated portions. Here, ‘treated portions’ ispreferably understood to mean portions in which material has beenremoved. One or more indentations, in particular recesses 6 and/orhollow cavities 6, thus preferably extend preferably orthogonally to thesurface and/or the crack-forming layer, starting from the surface 16 onwhich the stress-inducing layer 14 is arranged and which preferablyextends substantially or completely parallel to a crack-forming layerformed from modifications 10. Here, it is alternatively conceivable thatonly one indentation 6, in particular a hollow cavity and/or a recess,has been produced and/or is formed by means of material removal. Thematerial removal is preferably performed, in particular by means oflaser ablation, before the production or attachment of thestress-inducing layer 14 on the surface 16. The stress-inducing layer14, in the state coupled or connected to the solid body 2, covers theindentation(s) 6, in particular the hollow cavity or the hollow cavitiesor the recess or the recesses.

There is preferably no further coating, in particular no furthermaterial application, between the production of the indentation 6, inparticular the recess and/or the hollow cavity, and the attachment ofthe stress-inducing layer. This is advantageous since otherwise materialcould accumulate in the recess/hollow cavity.

The stress-inducing layer is preferably attached by means of a plasmalamination process. This is advantageous since a connection between thesolid body 1, in particular the main surface 16 of the later solid-bodylayer 1, and the stress-inducing layer 14 can thus be produced over theindentation 6, in particular recess/hollow cavity. The connection ispreferably a lamination or adhesive bonding. It is preferablyimplemented with use of cold plasma.

Additionally or alternatively, a “spontaneous split” with previouslyproduced laser plane or crack-forming plane and depth modification canbe brought about in accordance with the invention by a material removalstep, in particular laser ablation. This is preferably implementedwithout stress-inducing layer 14.

The stress-inducing layer 14 can also be referred to as a stressorlayer, in particular as a self-supporting stressor layer.

In accordance with the invention it has also been found that aself-supporting stressor layer is of significant technical advantagecompared to a stressor layer applied by vapour deposition or applied bysome other form of deposition, since stressor layers of this kind can beproduced on the one hand in larger volume in simpler methods inspecialised facilities with a higher throughput and on the other handcan be used in lamination processes, which likewise allow quickerprocess speeds. In addition, self-supporting stressor layers can also beremoved again from the substrate following lamination processes, evenwith little effort, which for example also allows re-use, i.e. of thestressor layer or of the stress-inducing layer, which is not possiblewith deposited layers.

It is particularly advantageous that lamination processes can also beperformed without adhesive bonding methods or the like purely by asurface activation, surface treatment, or surface modification of thesubstrate. A coupling or connection of the stress-inducing layer to thesolid body, in particular to the surface 16 of the later solid-bodylayer 1, is thus achieved particularly preferably by a surfaceactivation and/or surface treatment and/or surface modification of thesolid body or the surface 16 of the later solid-body layer 1.

For example, the surface can preferably be activated by contact with, inparticular in a chamber, produced ozone and/or by ultraviolet light of acertain wavelength and/or by plasma methods with different formedspecies on the surfaces of the substrate and/or the stressor layerand/or in the process gas, in particular radical aldehyde and alcoholspecies. Here, hot plasma methods are preferred in particular, in whichhigh temperatures are used in order to produce free charge carriers andradicals in the plasma, which, for the subsequent reactions at thesurfaces of substrate and stressor layer, allows other reaction pathsand chemical surface reactions compared to lower temperatures. Thesurface modification mechanism can thus differ in atemperature-dependent manner, also between various substrates, whereinfor example in the case of SiC, compared to Si, the carbon atomsinvolved can form different surface species in the plasma treatmentwhich can likewise have an adhesion-promoting effect in the laminationprocess.

Alternatively, the use of a cold plasma method is possible, in which aplasma is not produced by thermionic emission or via hot tungstenfilaments or similar methods, but instead via piezoelectric transformersat atmospheric pressure and preferably without elevated temperatures.These lower temperatures likewise reduce and/or change the availablereaction paths for surface activations and surface modifications foradhesion promotion in lamination processes, both at the substrate or thesolid body and at the stressor layer. The resultant surface species arethus dependent on a multiplicity of parameters and the surfaceactivation method in particular.

The surface treatment or modification for example comprises theexposure, at least in portions, of the surface to be treated by a coronatreatment and/or a flame treatment and/or a treatment by means ofelectrical barrier discharge and/or fluorination and/or by ozonisationand/or by excimer irradiation and/or by a treatment with a plasma,wherein individual or a plurality of physical parameters, such as thetype of plasma, the path distance during the plasma treatment, thenozzle type, the nozzle distance and/or the duration of the plasmatreatment, are preferably varied or can be varied.

A plasma pre-treatment or plasma treatment is preferably used both forcleaning and then for homogenisation of the surface species (for examplehydrophobising, amongst others).

A spatially resolved variation of the surface activation can be producedor adjusted by means of a selective individual plasma treatment and thenallows a lamination of the stressor layer, likewise with differentproperties in different areas, if desired.

The process of the plasma surface activation or of the plasma surfacetreatment allows a greater influencing in order to apply the desireddifferentiated adhesion or force transfer after the lamination of thestressor layer on the substrate also over large areas in a definedsymmetrical or asymmetrical form. Here, by means of process variation,an amended adhesion or cohesion can be set, in particular locally.Depending on the starting properties of the different solid-bodymaterials, in particular semiconductor materials, layers can be appliedand/or the desired auxiliary layer(s), in particular sacrificial/damagelayers or substrate and/or stressor layer surfaces, can be selectivelymodified (hydrophobic, hydrophilic, wetting, etc.) by further gradualprocess gases (oxygen, amongst others). This leads to a spatiallyresolved, adapted gradual adhesion or spatially resolved adapted oradjusted force transfer connection, also in lamination processes, whichis only homogeneous and not spatially resolved compared to that byadhesive bonding and deposition solutions for the stressor layer.

As already described, different physical parameters can be used duringthe plasma treatment (for example plasma type, path distance during theplasma treatment, nozzle type, nozzle distance, duration of the plasmatreatment). In addition to these influencing parameters, a greaterbandwidth of the necessary surface properties can be provided byselective admixing of gradual process gases, such as nitrogen, oxygen,hydrogen, SiH4, Si(EtO)4 or Me3SiOSiMe3 (amongst others). These resultpreferably from new chemical surface species, which deposit themselveson the semiconductor surface and/or the adjoining sacrificial layersand/or the stressor layer and thus enable a different surfacefunctionality and lamination process properties. This leads to thedesired target profiles, for example different spatially resolvedadhesion and cohesion properties, of the semiconductor surfaces and/orthe adjoining stressor and/or other layers.

A corona treatment is an electrochemical method for surface treatment ormodification of plastics. Here, the surface is exposed to an electrichigh-voltage discharge. A corona treatment is used for example topromote adhesion in plastics and films, amongst others (PE, PP).

In the case of a flame treatment a surface-near oxidation of therespective compounds takes place in particular. In principle, oxidationprocesses are performed, by means of which different polar functionalgroups are formed (for example oxides, alcohols, aldehydes, carboxylicacids, esters, ethers, peroxides) depending on the material and testconditions.

A treatment by dielectric barrier discharge (DBE, AC voltage gasdischarge, also DBD treatment) is similar to a low-temperature plasma orglow discharge (for example GDMS). In the case of DBE treatment thesurface is acted on by unipolar or bipolar pulses with pulse durationsof a few microseconds down to tens of nanoseconds and amplitudes in thesingle-digit kilovolt range. A dielectric barrier discharge isadvantageous since no metal electrodes are anticipated in the dischargechamber, and therefore no metal contaminations or electrode wear isanticipated.

Further advantages of the dielectric barrier discharge, depending onapplication, for example can be that it has a high efficiency, since nocharge carriers have to exit or enter at the electrodes (omission of thecathode drop, no glow emission necessary), or that the dielectricsurfaces can be modified and chemically activated at low temperatures.The surface modification is performed here preferably by an interactionand reaction of the surface species by ion bombardment and the effect ofultraviolet radiation on the surface species (for example 80 nm-350 nm,incoherent UV and VUV light, by high-frequency power generators). Thedielectric barrier discharge is used for example for in situ productionof ozone in drinking water/wastewater treatment, wherein the water isozonised by the ozone. Similarly, in the case of a surface treatment ormodification according to the invention by means of ozonisation, thesurface to be treated is acted on by ozone.

A surface treatment or modification by means of halogenation, inparticular fluorination, causes an element or a compound to be convertedinto a halide. By means of the fluorination, fluorine is thus introducedinto preferably organic compounds with the aid of fluorinating agents.

A surface treatment or modification by means of UV treatment isperformed preferably by excimer irradiation or by ultravioletlight-emitting diode sources, for example based on aluminium nitride.Excimer irradiation is performed by the use of at least one excimerLASER. Excimer LASERs are gas LASERs which can generate electromagneticradiation in the ultraviolet wavelength range. A gas discharge occurringin this case is thus caused by an electromagnetic high-frequency field.There is thus also no need for any electrodes for the gas discharge. Theproduced UV radiation lies preferably in a wavelength range between 120nm and 380 nm.

REFERENCE LIST

1 solid-body slice

2 donor substrate

4 surface extending in the peripheral direction

6 indentation

8 ablation LASER beams

10 modifications

11 detachment region

12 further LASER beams

14 stress-inducing layer

16 planar surface

17 edge

18 indentation end

20 crack

21 ablation tool

22 grinding tool

23 ring

24 first processing portion

34 secondary grinding face

36 first portion of LASER beams

38 first angle

40 further portion

42 second angle

44 edge

46 LASER device

48 LASER focus

50 peripheral delimiting face

1. A method for separating at least one solid-body layer, in particulara solid-body slice (1), from a donor substrate (2), said methodcomprising at least the following steps: providing a donor substrate(2), producing modifications (10) within the donor substrate (2) bymeans of LASER beams (12), wherein a detachment region is predefined bythe modifications (10), along which detachment region the solid-bodylayer (1) is separated from the donor substrate (2), removing materialfrom the donor substrate (2) starting from a surface (4) extending inthe peripheral direction of the donor substrate (2) in the direction ofthe centre (Z) of the donor substrate (2), in particular in order toproduce a peripheral indentation (6), wherein the detachment region isexposed by the material removal, separating the solid-body layer fromthe donor substrate, wherein the donor substrate is weakened in thedetachment region by the modifications in such a way that the solid-bodyslice (1) detaches from the donor substrate (2) as a result of thematerial removal or after the material removal, such a number ofmodifications are produced that the donor substrate is weakened in thedetachment region in such a way that the solid-body layer (1) detachesfrom the donor substrate (2), or a stress-inducing layer (14) isproduced or arranged on a surface (16) of the donor substrate (2), inparticular a planar surface, oriented at an incline relative to theperipheral surface, and mechanical stresses are produced in the donorsubstrate (2) by a thermal treatment of the stress-inducing layer (14),wherein the mechanical stresses produce a crack (20) for separating asolid-body layer (1), which crack propagates along the modifications(10), starting from the surface of the donor substrate exposed by thematerial removal.
 2. The method according to claim 1, characterised inthat the detachment region predefined by the modifications (10) isdistanced further from the peripheral surface of the donor substrate (2)prior to the material removal than after the material removal.
 3. Themethod according to claim 1 or claim 2, characterised in that themodifications (10) for predefining the detachment region are producedprior to the material removal, and by means of the material removal areduction of the distance of the detachment region to less than 10 mm,in particular to less than 5 mm and preferably to less than 1 mm, isachieved at least at specific points, or the modifications forpredefining the detachment region are produced after the materialremoval, wherein the modifications (10) are produced in such a way thatthe detachment region is distanced, at least at specific points, by lessthan 10 mm, in particular less than 5 mm, and preferably less than 1 mm,from a surface exposed by the material removal.
 4. The method accordingto any one of the preceding claims, characterised in that the materialis removed by means of ablation beams (8), in particular ablation LASERbeams, or ablation fluids or an indentation (6) with an asymmetricaldesign is produced by the material removal or the material removal isperformed at least in portions in the peripheral direction of the donorsubstrate (2) as a reduction of the radial extent of the donor substrate(2), in the entire region between the detachment region and a surface ofthe donor substrate (2) distanced homogeneously from the detachmentregion.
 5. The method according to claim 4, characterised in that theindentation (6) surrounds the donor substrate (2) completely in theperipheral direction.
 6. The method according to claim 4 or claim 5,characterised in that the indentation (6) runs towards the centre (Z) asfar as an indentation end (18) in a manner becoming increasinglynarrower, in particular in a wedge-like manner, wherein the indentationend (18) lies in the plane in which the crack (20) propagates.
 7. Themethod according to any one of the preceding claims, characterised inthat the asymmetric indentation (6) is produced by means of a grindingtool (22) that is negatively shaped at least in part in order to makethe indentation (6).
 8. The method according to claim 7, characterisedin that the grinding tool (22) has at least two differently shapedprocessing portions (24, 26), wherein a first processing portion (24) isintended for processing of the donor substrate (2) in the region of theunderside (28) of a solid-body slice (1) to be separated and a secondprocessing portion (26) is intended for processing of the donorsubstrate (2) in the region of the upper side (30) of the solid-bodyslice (1) to be separated from the donor substrate (2).
 9. The methodaccording to claim 8, characterised in that the first processing portion(24) produces a deeper or larger-volume indentation (6) in the donorsubstrate (2) than the second processing portion (26), wherein the firstprocessing portion (24) and/or the second processing portion (26)have/has curved or straight grinding faces (32, 34).
 10. The methodaccording to claim 9, characterised in that the first processing portion(24) has a curved main grinding face (32) and the second processingportion (26) has a curved secondary grinding face (34), wherein theradius of the main grinding face (32) is greater than the radius of thesecondary grinding face (34), the radius of the main grinding face (32)is preferably at least twice as large as the radius of the secondarygrinding face (34) or the first processing portion (24) has a straightmain grinding face (32) and the second processing portion (26) has astraight secondary grinding face (34), wherein, by means of the maingrinding face (32), more material is removed from the donor substrate(2) than with the secondary grinding face (34) or the first processingportion (24) has a straight main grinding face (32) and the secondprocessing portion (26) has a curved secondary grinding face (34) or thefirst processing portion (24) has a curved main grinding face (32) andthe second processing portion (26) has a straight secondary grindingface (34).
 11. The method according to any one of the preceding claims,characterised in that the ablation LASER beams (8) are produced with awavelength in the range between 300 nm and 10 μm, with a pulse length ofless than 100 microseconds and preferably less than 1 microsecond, andparticularly preferably less than 1/10 of a microsecond, and with apulse energy of more than 1 μJ and preferably more than 10 μJ.
 12. Themethod according to claim 4, characterised in that the material to beremoved in the entire region between the detachment region and thesurface distanced homogeneously from the detachment region describes anannular, in particular cylindrical design.
 13. The method according toany one of preceding claims 1 to 8, characterised in that wherein theLASER beams (12) are emitted from a LASER device (46), wherein the LASERdevice (46) is a picosecond laser or a femtosecond laser, and/or theenergy of the LASER beams (12), in particular of the fs-LASER, isselected in such a way that the propagation of damage of eachmodification (10) in the donor substrate (2) is less than 3 times theRayleigh length, preferably less than the Rayleigh length, andparticularly preferably less than a third of the Rayleigh length and/orthe wavelength of the LASER beams (12), in particular of the fs LASER,is selected in such a way that the absorption of the donor substrate (2)is less than 10 cm⁻¹ and preferably less than 1 cm⁻¹ and particularlypreferably less than 0.1 cm⁻¹ and/or the individual modifications (10)are produced in each case as a result of a multi-photon excitationbrought about by the LASER beams (12), in particular of the fs LASER.14. The method according to claims 1 to 9, characterised in that theLASER beams (12) for production of the modifications (10) penetrate thedonor wafer (2) via a surface (16) that is part of the solid-body slice(1) to be separated.
 15. The method according to any one of thepreceding claims, characterised in that the stress-inducing layer (14)comprises a polymer, in particular polydimethylsiloxane (PDMS), orconsists thereof, wherein the thermal treatment is performed in such away that the polymer experiences a glass transition, wherein thestress-inducing layer (14) is temperature-controlled, in particular bymeans of liquid nitrogen, to a temperature below room temperature orbelow 0° C. or below −50° C. or below −100° C. or below −110° C., inparticular to a temperature below the glass transition temperature ofthe stress-inducing layer (14).
 16. The method according to any one ofthe preceding claims, characterised in that the ablation radiationcomprises accelerated ions and/or plasma and/or LASER beams and/or isformed by electron beam heating or ultrasound waves and/or is part of alithographic method (electron beam, UV, ions, plasma) with at least oneetching step following a previously executed photoresist coating and/orthe ablation fluid is a liquid jet, in particular a water jet of a waterjet cutting process.